Capacitive pressure transducer systems of the type described in the preceding paragraph are generally known in the prior art; and prior art transducers of this type are disclosed in U.S. Pat. No. 4,735,098, granted Apr. 5, 1988, to inventors Fred Kavli and Kyong Park; and U.S. Pat. No. 4,425,797, granted Jan. 17, 1984 to inventor Kyong Park, with both patents being assigned to Kavlico Corporation, the assignee of the present invention.
In pressure measurement systems using transducers of this general type, normal performance checks have occasionally indicated incorrect output results. In one known system, a square wave is applied to a first circuit including a fixed reference capacitor and to a second circuit including a pressure variable capacitor which may be the conductive plates associated with a pressure responsive diaphragm. The output from each of the first and the second circuit varies with the value of the capacitance, and the difference between the two outputs is measured to indicate the level of the pressure applied across the diaphragm. In the cases where the normal performance checks indicated incorrect voltage versus pressure outputs, in some cases a very low output reading was observed at all times indicating zero input pressure despite high applied pressure levels, and in other cases the output voltage would drift up or down, indicating high or low pressure regardless of the actual applied pressure.
A principal object of the invention is to provide a more stable pressure transducer system which is not subject to the problems outlined above despite adverse conditions.